Storage system, backup system, and backup method

ABSTRACT

A storage controller can perform backup processing without proceeding via a server and without the need for the server to grasp the state of pair volumes. When an instruction for backup is given from the server while data is being copied from a source volume to a target volume, the storage controller transfers the data to a backup device using differential information between the pair volumes after waiting until data about a range to be backed up and instructed by the server is copied into the target volume.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application relates to and claims priority from JapanesePatent Application No. 2003-183742, filed on Jun. 27, 2003, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to the backup ofinformation stored in a storage system, and, more particularly, toserver-free backup of information on a storage area network (SAN).

[0003] As computer systems have treated an increasing amount ofinformation in recent years, there is an increasing need for backing upsuch information. Thus, there is a tendency for the load imposed onbackup processing of a server to be increased. Where a server backs up alarge amount of data, the data is read from a storage system with whicha source storage device to be backed up is connected, and then the datais written into a target backup device, such as a tape library, forexample.

[0004] However, as the amount of data increases, the server resources(e.g., host bus adapter) used for the backup are occupied for a longertime. Thus, if another application program tries to use this host busadapter to send and receive other data during this interval, theprocessing has to wait for a long time or the performance deterioratesgreatly.

[0005] One means for alleviating the burden imposed on a server's backupprocessing to solve the above-described problems involves the backup ofdata using an Extended Copy command.

[0006] On the other hand, in an application where there is a largeamount of I/O processing to and from a storage volume, in a case wherethe server issues a splitting instruction to pair volumes, an updatecopy from the source volume to the target volume may not be immediatelyended. Rather, some time is taken until a split state is reached. Tosolve this problem, there is a technique that is available. Inparticular, when a server issues a splitting instruction to pairvolumes, a storage controller continues an update copy to the targetvolume, while responding to the server that the pair volumes are in asplit state.

[0007] Patent Reference 1: JP-A-2001-222355

[0008] Patent Reference 2: JP-A-2002-366310

[0009] However, where data is transferred to a backup device that isdifferent from the server, it is only assured that the data in thestorage device will be transferred to the server. Therefore, theconsistency between the data transferred from the target volume to thebackup device and the data in the source volume is not assured.

[0010] Furthermore, if a backup is performed after waiting until data tobe updated is completely reflected in the target volume from the sourcevolume, the server waits without being capable of giving an instructionfor start of backup processing until the data to be updated iscompletely reflected in the target volume. The server needs to monitorthe split state.

SUMMARY OF THE INVENTION

[0011] Accordingly, it is an object of the present invention to providea technique which makes it possible to respond to a server that pairvolumes are in a split state. The technique also assures consistency ofdata even in a case where the data is transferred to a backup deviceusing a backup command, and it enables backup without urging theserver's processing to wait.

[0012] A storage system that achieves this object has a storagecontroller and a storage device. The storage controller has a memory,together with first, second, third, and fourth control portions. Thestorage device has first and second storage units. The first controlportion of the storage controller stores information into the firststorage unit via the memory. The control portion that actually storesinformation into the storage unit is the third control portion. Thefirst storage unit is a source volume. The second storage unit is atarget volume. Furthermore, the third control portion stores informationfrom the first storage unit into the second storage unit.

[0013] On the other hand, when an instruction for pair splitting isgiven from the server, the storage controller writes differentialinformation between the first and second storage units into the memory.Also, the pair splitting is reported to the first server. Then, where abackup command is subsequently received from the second server, thefourth control portion transfers data to be backed up to a backup devicebased on the differential information between the pair volumes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a block diagram of a client server, a backup server, anda storage system;

[0015]FIG. 2 is a diagram showing a table on a common memory necessaryto check backup processing and differential data between pair volumes,as well as a data storage area;

[0016]FIG. 3 is a conceptual block diagram of a first embodiment;

[0017]FIG. 4 is a flowchart of the processing carried out in the firstembodiment;

[0018]FIG. 5 is a conceptual block diagram of a second embodiment;

[0019]FIG. 6 is a flowchart of the processing carried out in the secondembodiment;

[0020]FIG. 7 is a conceptual block diagram of a third embodiment;

[0021]FIG. 8 is a conceptual block diagram showing a modification of thethird embodiment;

[0022]FIG. 9 is a flowchart of the processing carried out in the thirdembodiment;

[0023]FIG. 10 is a conceptual block diagram of a fourth embodiment; and

[0024]FIG. 11 is a flowchart of the processing carried out in the fourthembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention will be hereinafter with reference to thedrawings.

[0026] First Embodiment

[0027]FIG. 1 is a diagram showing the configuration of a storage system300 in a first embodiment of the present invention. In the storagesystem 300, a storage controller 301 is connected with a client server101 via a switch 304 by paths 201 and 206, and it controls I/Oprocessing required from the client server 101. Similarly, the storagecontroller 301 is connected with a backup server 102 via the switch 304by paths 202 and 203, and it controls I/O processing required from thebackup server 102. Furthermore, the storage controller 301 is connectedby paths 204 and 205 via the switch 304 with a tape device 303, thatconstitutes a backup device, and it controls I/O processing to and fromthe tape device 303. The client server 101, backup server 102, storagecontroller 301 and backup device 303 are connected via the switch 304.The switch 304 controls the route of the paths. For example, when theclient server 101 issues a command to a channel port 401, the commandsent from the client server 101 via a path is analyzed in terms of thedestination address by the switch 304. The shortest route is selectedand the command is routed. In this case, the command reaches the channelport 401 via the path 206.

[0028] The client server 101 and backup server 102 are connected by theLAN 206. The servers 101 and 102 communicate with each other to controlthe parameters/timing of commands of pair split and instruction commandsfor backup. The pair splitting commands and instruction commands forbackup are issued from backup software 105 and 106, and they are sent tothe storage controller 301 via drivers 103 and 104, respectively. Theprocessing of the client server 101 and backup server 102 may beperformed all by the client server 101. Conversely, the backup server102 may perform all of the processing of the client server 101.

[0029] The storage controller 301 has I/O processing control portions(I/O processors) 501-503 for performing I/O processing with the clientserver 101 and backup server 102 via the channel ports 401-403. Also,the storage controller 301 has an I/O processing control portion (I/Oprocessor) 508 for performing I/O processing with volumes. The, I/Oprocessors 501-503 and 508 can operate independently. For example, theI/O processor 501 performs I/O processing from the client server 101. Onthe other hand, the I/O processor 508 independently performs I/Oprocessing between a common memory/cache memory 507 and a storage device302. The common memory/cache memory 507 is a memory that can be accessedfrom the I/O processors 501-503.

[0030] The I/O processors 501-503 and 505 have individual memories504-506 and 509, respectively, that store respective controlinformation. These individual memories cannot be accessed from pluralI/O processors. In contrast, the common memory/cache memory 507 cantemporarily store data from servers and data from the storage device302, as well as control information that can be shared among the I/Oprocessors 501-503 and 508.

[0031] The storage device 302 that is connected with the storagecontroller 301 has a source volume 601, a target volume 602, a volume603 for pair operation, and a volume 604 for backup processing. The I/Oprocessor 508 directly performs I/O processing on each volume of thestorage device 302. For instance, where the I/O processor 501 writesWrite data from the client server 101 into the source volume 601, theI/O processor 501 once stores the Write data into the commonmemory/cache memory 507. At this stage, the I/O processor 501 reportscompletion of writing to the client server 101. Then, the I/O processor501 performs other I/O processing. Meanwhile, the I/O processor 508performs polling- at regular intervals on the common memory/cache memory507. Where the Write data is stored in the common memory/cache memory,the I/O processor 508 writes the Write data into the source volume 601.Because of the above-described I/O processing, I/O processing includingreading and writing is performed between the client server 101 andsource volume 601.

[0032] When the source volume 601, in which the data in the clientserver 101 has been stored, is backed up to the tape device 303, it isnecessary to create a copy of the source volume 601 into the targetvolume 602 within the storage device 302, because if the storagecontroller 301 attempts to perform a backup from the source volume tothe tape device directly, the I/O processing from the client server 101that is normal processing becomes deteriorated. Alternatively, it isnecessary to stop the I/O processing.

[0033] The source volume 601 and target volume 602 that form a pair ofvolumes can take the following states:

[0034] (1) Simplex state: A pair of a source volume and a target volumeis not formed.

[0035] (2) Duplex pending state (transient duplex state): After a sourcevolume and a target volume form a pair, creation copy processing andupdate copy processing are carried out or might be carried out. Thecreation copy process referred to herein involves a copy of data fromthe source volume to the target volume and occurs when a copy of datafrom the source volume to the target volume is started, but both are notyet in a fully mirrored state. On the other hand, the update copyprocess involves a copy of data from the source volume to the targetvolume and occurs when data is written into the source volume eitherbefore the source and target volumes assume a fully mirrored state orafter they have reached a fully mirrored state.

[0036] (3) Duplex state: After source and target volumes form a pair,the creation copy process is complete, and the source and target volumesare in a fully mirrored state. However, an update copy of data from thesource volume to the target volume might be carried out.

[0037] (4) Split state: This is a state obtained after the pair ofsource and target volumes has been split.

[0038] (5) Split pending state (transient split state): After the pairof source and target volumes has been split, differential data that isto be updated from the source volume to the target volume still exists.An update copy process is carried out.

[0039] A copy process can be performed from a source volume to a targetvolume by making transitions between the above-described states. In thepresent embodiment, assignments to the source volume 601 and targetvolume 602 are stored in source volume number 512 and target volumenumber 513 of the common memory/cache memory 507 shown in FIG. 2.Furthermore, a backup processing-and-management area 510, that ismanaged by the common memory/cache memory 507, has the following: backupparameter information 511 for storing parameter information about abackup, source volume number 512, target volume number 513, pair volumedifference information 514, pair state information (source volume) 516,and pair state information (target volume) 517. In addition, the cachememory has a backup data storage area 515 for storing backup data readfrom a specified area. The pair state information (source volume) 516and pair state information (target volume) 517 are available as meansfor knowing whether differential data is reflected or not. If a pairsplit is performed, the pair state information (source volume) 516immediately becomes “pair split”, but the pair state information (targetvolume) 517 remains in “transient pair split” state until thedifferential data is reflected in the target volume. Therefore, it ispossible to know whether the differential data has been reflected, fromthis-information, the storage controller 301, and servers 101, 102.

[0040]FIG. 3 is a conceptual block diagram illustrating a summary of thebackup processing in the present embodiment. For the sake of simplicity,the switch 304, I/O processors 501-503, 508, etc. are omitted in FIG. 3.The storage controller 301 is a conceptual diagram of backup processingin a case where differential data from the source volume 601 to thetarget volume 602 exists after the pair volumes have been split. If aninstruction command for backup is issued from the backup server 102after the pair splitting, the storage controller 301 checks to see ifdifferential data remains in the range to be backed up. Wheredifferential data remains, the storage controller 301 reflects thedifferential data concerning the portion to be backed up in the targetvolume 602 and then transfers the backed-up data to the tape device 303.This permits the processing to proceed without producing a wait time inthe backup processing.

[0041]FIG. 4 is a flowchart illustrating a summary of the processingcarried out in the present embodiment. It is assumed that a creationcopy or update copy is made from a source volume to a target volume. (1)The backup server 102 issues an instruction command for starting abackup to the client server 101. (2) The client server 101 receiving thecommand issues an instruction command for splitting the pair volumes tothe I/O processor 501. Then, the I/O processor 501 causes the pair stateinformation (source volume) 516 to pair split. (3) Also, the I/Oprocessor 501 reports the end of the splitting of the pair volumes tothe client server 101. In this state, pair state information (targetvolume) 517 is in a pending pair split state. Subsequently, theprocessor 501 issues a command to the processor 508 based on the pairvolume difference information 514 to perform a copy of data from thesource volume to the target volume. The I/O processor 508 receiving thecommand executes a copy of data into the target volume 602 according tothe pair volume difference information 514 that manages the data notreflected from the source volume 601 to the target volume 602 at theinstant of the pair splitting, until the data in the source volume 601agrees with the data in the target volume 602. Here, the processor 508operates independently of the processing of the processors 501-503.

[0042] Meanwhile, (4) the client server 101 receiving the report of theend of the splitting reports the completion of the splitting of the pairvolumes to the backup server 102. (5) The backup server 102 receivingthe report of the completion of the splitting of the pair volumes issuesan instruction command for backup to the I/O processor 502. Theprocessor 502 receiving the instruction command for backup analyzes thebackup instruction command and stores the results of the analysis in thebackup parameter information 511. An example of this backup parameterinformation includes parameters of an Extended Copy command that is aSCSI standard. Volume information about the source volume, volumeinformation about the backup destination, and information describing therange backed up are contained in the parameters. Then, an instructioncommand for the backup is reported to the processor 503. Here, the I/Oprocessors 502 and 503 are assigned to two I/O processors and the I/Oprocessing is performed to distribute the load. Also, the channel portsare divided into two, i.e., channel ports 402 and 403, to secure thecommunication bandwidth for the paths.

[0043] The I/O processor 503, upon receiving the Backup instructioncommand from the I/O processor 502, checks the pair volume differenceinformation 514 to confirm whether all of the range to be backed up oreach unit of data to be written into the backup device has been copiedfrom the source volume 601 to the target volume 602 by referring to thebackup parameter information 511. Where the differential data about therange to be backed up does not exist in the pair volume differenceinformation 514, the processor 503 reads data to be backed up from thetarget volume into the cache memory. Then, backup to the tape device 303is started. Meanwhile, (6) where the I/O processor 503 refers to thebackup parameter information 511 and the differential data about therange to be backed up is present in the pair volume differenceinformation 514, the I/O processor 503 gives an instruction to the I/Oprocessor 508 to copy the differential data. The I/O processor 508receiving the instruction performs a copy operation with a priority onthe differential data about the range to be backed up. After thecompletion of the copy operation, the I/O processor 508 reports thecompletion of the copy of differential data about the range to be backedup to the I/O processor 503.

[0044] (7) The I/O processor 503 receiving the report backs up the dataabout the range to be backed up to the tape device 303. After completionof the backup, the processor 503 reports the end of the backup to theprocessor 502. (8) The processor 502, upon receiving the report of theend, reports the end of the backup to the backup server 102, thus endingthe backup.

[0045] After the end of the backup, the I/O processor 508 continues tocopy until a duplex state is reached, i.e., the source and targetvolumes agree in data content.

[0046] The present embodiment makes it unnecessary for the backup server102 to wait for pair splitting of the target volume 602. Furthermore,the backup server 102 does not need to monitor the state of the pairsplits. Hence, the load on the backup server 102 can be reduced.

[0047] Second Embodiment

[0048]FIG. 5 is a conceptual block diagram of backup processing inaccordance with a second embodiment. After pair splitting, if the backupserver 102 issues an instruction command for backup, the storagecontroller 301 checks to see if differential data remains in the rangeto be backed up. Where differential data remains, the I/O processor 503makes the backup command wait until all the differential data has beencopied into the target volume 602. As a result, it takes a long timeuntil the backup processing is completed, but the processing in thestorage controller 301 is made simpler. In addition, the backupprocessing can be made to proceed without the client server 101 andbackup server 102 monitoring the state of the target volume 602.

[0049]FIG. 6 is a flowchart illustrating a summary of the processing.The processing is almost identical with the first embodiment. Thedifference from the first embodiment is that the I/O processor 503monitors the state of reflection of the differential data between thepair volumes and starts backup processing after all of the differentialdata has been reflected in the target volume.

[0050]FIG. 7 shows a modification of the present embodiment,illustrating processing in a case where the backup software 106 for thebackup server 102 monitors the differential data, instead of the storagecontroller 301 in FIG. 5. In FIG. 5, after pair splitting, the sourcevolume 601 of the pair of volumes quickly assumes a state of “pairsplit”. On the other hand, the target volume 602 remains in the“pending-split state” until all of the differential data is reflected inthe target volume. Therefore, it is impossible to perform backupprocessing. However, the backup server 102 can check to see whether ornot the differential data is reflected in the target volume 602.Therefore, the server periodically checks the state. After confirmingthat the “pair split state” has been reached, the backup server 102 canissue a Backup Start command. In this modified embodiment, the backupserver 102 can control the backup processing instead of monitoring thestate of the target volume 602 by the I/O processor 503.

[0051] Third Embodiment

[0052]FIG. 8 is a conceptual block diagram illustrating the manner inwhich backup processing is performed using the backup data storage area515 in a case where differential data exists from the source volume 601to the target volume 602 after the pair volumes have been split inbackup processing.

[0053] After pair splitting, if an instruction command for backup isissued from the backup server 102, the storage controller 301 checks tosee whether differential data remains in the range to be backed up.Where differential data remains, the storage controller 301 reads thedifferential data concerning the portion to be backed up from the sourcevolume 601 and once stores the data into the backup data storage area515. Furthermore, if the data about the range to be backed up has beenreflected in the target volume 602, the data is read into the backupdata storage area 515 and merged with the data from the source volume601. Then, the merged data is transferred to the tape device 303. Thus,even where there is differential data in the same way as in the firstembodiment, the processing can be made to proceed without producing await time in the backup processing. Since differential data is notreflected in the target volume 602, the backup processing can beperformed at a correspondingly higher rate.

[0054]FIG. 9 represents a flowchart illustrating a summary of processingin the present embodiment. The processing in the present embodiment isalmost identical with the first embodiment. The differences are asfollows. Where the I/O processor 503 checks the state of reflection ofthe differential data between the pair volumes and finds that the datais not reflected, data is read from the source volume 601 to the backupdata storage area 515. After data about the range to be backed up isfully read into the backup data storage area 515, the I/O processor 503transfers data about the range to be backed up to the tape device 303.Meanwhile, where data about the range to be backed up all exists in thetarget volume, the I/O processor 503 reads the data about the range tobe backed up from the target volume 602 into the backup data storagearea 515 and then transfers the data to the tape device 303. Where thedifferential data is not reflected in the target volume, data is storeddirectly into the backup data storage area 515 without writing the datainto the target volume 602 by this method and so data about the range tobe backed up can be prepared quickly.

[0055] Fourth Embodiment

[0056]FIG. 10 is a conceptual block diagram illustrating processing in acase where a Pair Splitting instruction command and a Backup instructioncommand are combined into one command in backup processing. In thepresent embodiment, the client server 101 does not need to issue a PairSplitting instruction command, unlike the aforementioned embodiments.Instead, the backup server 102 first reports the start of a backup tothe client server 101 via the LAN 205. Because of this report, theclient server 101 temporarily interrupts normal I/O processing andresponds to the backup server 102 regarding the start of the backup. Thebackup server 102 subsequently issues a Backup instruction command tothe storage controller 301 without monitoring the paired state of thevolumes. On receiving the Backup command, the storage controller 301gives an instruction for canceling the first specified paired state. Atthis instant, the controller responds to the Backup command. The backupserver 102 receives the response from the storage controller 301 andmakes a report for resumption of I/O processing to the client server101. After receiving the report, the client server 101 resumes the I/Oprocessing.

[0057] Meanwhile, the storage controller 301 that has given aninstruction for pair splitting then reflects the differential data aboutthe range to be backed up in the target volume 602.and transfers thebacked-up data to the tape device 303. Because the backup server 102monitors the state of the backup in the storage controller, the backupserver 102 can know the end of the backup. ‘For example, the backupserver 102 checks the state by issuing a command for checking the statusof backup processing, such as a Receive Copy Result command, to thestorage controller 301.

[0058]FIG. 11 represents a flowchart illustrating the processing of FIG.6 summarily. The backup server 102 issues an instruction command forstarting a backup to the client server 101. The client server 101receiving the Backup Start instruction interrupts the normal I/Oprocessing temporarily. The normal I/O processing is interrupted becausethe processing for splitting the pair volumes is performed quickly. Theclient server 101 that has temporarily interrupted the I/O processingreports the interruption to the backup server 102. The backup server 102receiving the report issues an instruction command for splitting pairvolumes to the I/O processor 502. The I/O processor 502 receiving theBackup instruction command issues an instruction command for splittingpair volumes to the I/O processor 508. Then, the I/O processor 508performs processing independently of the I/O processors 502 and 503 inthe background and copies differential data into the target volume.

[0059] Meanwhile, the I/O processor 502 brings the pair stateinformation (source volume) 516 into a pair split state and brings thepair state information (target volume) 517 into a pending split stateand then reports the end of the splitting to the backup server 102.Furthermore, the I/O processor 502 makes a report of the Backupinstruction command to the I/O processor 503. Where the differentialdata about the range to be backed up does not exist in the targetvolume, the I/O processor 503 reflects the differential data about therange to be backed up from the source volume to the target volume. Then,the I/O processor 503 transfers the data about the range to be backed upto the tape device 303. Other processing is almost identical with theprocessing in the first embodiment.

[0060] In the present embodiment, backup processing can be performedwithout for the client server 101 or backup server 102 monitoring thestate of the pair volumes.

[0061] In the present embodiment, in a case where the data concerningthe range to be backed up is not reflected in the target volume, the I/Oprocessor 503 stores the data into the backup data storage area 515, andthen it can transfer the data to the tape device 303. Furthermore, theI/O processor 503 can make the transfer to the tape device 303 waituntil the differential data is fully copied into the target volume.

[0062] While the invention made by the present inventor has beendescribed in detail based on various embodiments, it is obvious that theinvention is not limited to the above-described embodiments, but can bemodified variously without departing from the gist thereof.

[0063] For example, in accordance with the present invention, a LAN isused as the network between the client server 101 and backup server 102.The network is not limited to a LAN. It may also be a fiber channel,telephone network, wireless network, or the like.

[0064] In addition, in accordance with the invention, the I/O processor508 is used for processing on the storage device 302. For this I/Oprocessing, the I/O processors 501-503 can be used.

[0065] Furthermore, in accordance with the invention, the volume 603 forpair operation and the volume 604 for backup processing can be definedon the common memory/cache memory without using actual volumes.

[0066] Additionally, in accordance with the invention, the backup deviceis not limited to the tape device 303. It may also be another type ofstorage device, such as a disk device.

[0067] Further, in accordance with the invention, the client server 101and backup server 102 can be combined into one server. Also, instead ofa server, a host can be used.

[0068] According to the present invention, one can obtain the advantagethat backup processing from a server can be performed after respondingto the server that pair volumes have been split and maintaining theconsistency in data between source and target volumes.

1. A storage system comprising: a first storage unit for storinginformation from a first server; a second storage unit for storing theinformation stored in said first storage unit; a storage deviceconnected with said first storage unit and with said second storage unitand with said first server and with a second server instructing saidfirst server another storage device connected with said second storageunit; and a storage controller for controlling said storage devices;wherein when an instruction for splitting is received from said firstserver, said storage controller reports end of the splitting to saidfirst server, receives an instruction for backup from said secondserver, and then transfers information to a backup device from saidsecond storage unit after copy of information from said first storageunit to said second storage unit ends.
 2. A storage system as set forthin claim 1, wherein information is transferred from said second storageunit to said backup device after copy of all information from said firststorage unit to said second storage unit ends.
 3. A storage system asset forth in claim 1, wherein when there is a request for transfer offirst information stored in said second storage unit and secondinformation not stored from said first storage unit into said secondstorage unit to the backup device, said second information is storedfrom said first storage unit into said first storage unit and then saidfirst information and said second information are transferred from saidsecond storage unit to said backup device.
 4. A storage system as setforth in claim 1, wherein when there is a request for transfer of firstinformation stored in said second storage unit and second informationnot stored from said first storage unit into said second storage unit tothe backup device, said first information is stored from said secondstorage unit into a memory that is connected with said storagecontroller unit and acts to store information and said secondinformation is stored from said first storage unit, and then said firstinformation and said second information stored in said memory aretransferred to said backup device.
 5. A backup method for a storagesystem having a first storage unit for storing information from a firstserver, a second storage unit for storing the information stored in saidfirst storage unit, a storage device connected with said first storageunit and with said second storage unit and connected with said firstserver and with a second server instructing said first server, and astorage controller for controlling said storage device, said methodcomprising the steps of: causing said first server to issue aninstruction for splitting to said storage controller; then causing saidstorage controller to report end of the splitting to said first server;and then, when an instruction for backup is received from said secondserver, transferring information from said second storage unit to abackup device after end of copy of the information from said firststorage unit to said second storage unit.
 6. A backup method as setforth in claim 5, wherein when there is a request from said secondserver for transfer of information stored in said second storage unit tothe backup device, the information is transferred to said backup devicefrom said second storage unit after end of copy of the whole informationinto said second storage unit from said first storage unit.
 7. A backupmethod as set forth in claim 5, wherein when there is a request fortransfer of first information stored in said second storage unit andsecond information not stored from said first storage unit into saidsecond storage unit to the backup device, said second information isstored from said first storage unit into said second storage unit, andsaid first information and said second information are transferred fromsaid second storage unit to said backup device.
 8. A backup method asset forth in claim 5, wherein when there is a request for transfer offirst information stored in said second storage unit and secondinformation not stored from said first storage unit into said secondstorage unit to the backup device, said first information is copied fromsaid second storage unit into a memory that is connected with saidstorage controller and acts to store information and said secondinformation is copied from said first storage unit, and said firstinformation and said second information stored in said memory aretransferred to said backup device.
 9. A backup system comprising:servers for storing information; a first storage unit for storinginformation from said servers; a second storage unit for copying theinformation stored in said first storage unit; and a storage controllerconnected with said servers, said first storage unit, and said secondstorage unit and controlling said first and second storage units;wherein when said storage controller receives an instruction forsplitting from said servers, end of splitting is reported to saidservers, an instruction for backup is received from said servers, theninformation is copied from said first storage unit into said secondstorage unit, and after the end thereof the information is transferredfrom said second storage unit to the backup device.
 10. A backup systemas set forth in claim 9, wherein said servers have a first server forissuing the instruction for splitting and a second server for issuingthe instruction for backup.
 11. A backup system as set forth in claim 9,wherein information is transferred from said second storage unit to saidbackup device after copy of whole information from said first storageunit to said second storage unit ends.
 12. A backup system as set forthin claim 9, wherein when there is a request for transfer of firstinformation stored in said second storage unit and second informationnot stored from said first storage unit into said second storage unit tothe backup device, said second information is copied from said firststorage unit into said second storage unit and then said firstinformation and said second information are transferred from said secondstorage unit to said backup device.
 13. A backup system as set forth inclaim 9, wherein when there is a request for transfer of firstinformation stored in said second storage unit and second informationnot stored from said first storage unit into said second storage unit tothe backup device, said first information is stored from said secondstorage unit into a memory that is connected with said storagecontroller and acts to store information and said second information isstored from said first storage unit, and then said first information andsaid second information stored in said memory are transferred to saidbackup device.
 14. A storage system comprising storage units and astorage controller for controlling said storage units; wherein saidstorage units include first and second storage units; and wherein saidstorage controller has (a) a memory, (b) a first control portionconnected with said memory, accepting splitting processing sent from afirst server, and reporting end of splitting to said first server, (c) asecond control portion connected with said memory and accepting backupprocessing sent from a second server after said report of end of thesplitting, (d) a third control portion connected with said storage unitsand with said memory and acting to copy information from said firststorage unit to said second storage unit, and (e) a fourth controlportion connected with said memory and accepting said backup processing,said fourth control portion transferring information from said secondstorage unit to a backup device after end of copy of information fromsaid first storage unit to said second storage unit.
 15. A storagesystem as set forth in claim 14, wherein information is transferred fromsaid second storage unit to said backup device after end of copy ofwhole information from said first storage unit to said second storageunit.
 16. A storage system as set forth in claim 14, wherein when thereis a request for transfer of first information stored in said secondstorage unit and second information not stored from said first storageunit into the second storage unit to the backup device, said secondinformation is stored from said first storage unit into said firststorage unit, and then said first information and said secondinformation are transferred from said second storage unit to said backupdevice.
 17. A storage system as set forth in claim 14, wherein whenthere is a request for transfer of first information stored in saidsecond storage unit and second Information not stored from said firststorage unit into said second storage unit to the backup device, saidfirst information is stored from said second storage unit into a memoryconnected with said storage controller and acting to store informationtemporarily, and wherein said first information and said secondinformation stored in said memory are transferred to said backup deviceafter said second information is stored from said first storage unit.